1. Field of the Invention
The present invention relates to the desulfurization of hydrocarbon streams. More specifically, the present invention relates to desulfurization of fuel gas hydrocarbon streams by converting organic sulfur compounds in the streams to hydrocarbon sulfide without added hydrogen.
2. Description of Prior Art
Stringent requirements will be set on refinery fuel gas to lower levels of sulfur, and thus minimize SOx emissions upon burning. Fuel gas sulfur levels as low as 40 ppm are contemplated in California while limits of 100 ppm may be imposed elsewhere in the United States.
Refinery fuel gases are typically purified before further treatment. This would normally involve the removal of hydrogen sulfide and mercaptans by means of alkaline absorbents, particularly alkanolamines, followed by sulfur production in a Claus process.
Solvents used for hydrogen sulfide absorption include aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and diisopropanolamine (ADIP). These differ in volatility and selectivity for the removal of hydrogen sulfide, mercaptans, and carbon dioxide from gases of different composition. Other alkaline solvents used for absorption of acidic components in gases include potassium carbonate solutions with activators and solubilizers to improve gas/liquid contacting, sodium phenate and several other organic compounds (Alazid) and alkaline phosphates. In most of these sulfur is separated as concentrated hydrogen sulfide gas. However, in the Stretford process, an hydrogen sulfide saturated anthraquinone disulphonate solution is oxidized with air to produce elemental sulfur, which is precipitated and removed by filtration.
These fuel gas streams may be further desulfurized by passing the gas over a bed of molecular sieves or synthetic zeolites. Impurities are retained in the bed. When the bed is saturated, it is regenerated by passing hot clean gas or hot nitrogen, generally in a reverse direction.
Although conventional amine-based absorbers are very effective in removing hydrogen sulfide, these absorbers are much less efficient in reducing organic sulfur compounds such as COS and RSH.